<!doctype html>
<html lang="zh-cn">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>CSS三角制作原理</title>

    <style>
        .box1 {
            width: 0;
            height: 0;
            border-width: 50px;
            border-style: solid;
            border-color: red blue green black;
            margin: 100px auto;
        }


    </style>
</head>
<body>
<div class="box1"></div>
</body>
</html>